CALCULATION AND EXPERIMENTAL CHARACTERIZATION OF THE DEFECT PHYSICS IN CuInSe 2 Jochen Klais 1 , Hans Joachim Möller 1 , David Cahen 2 1 TU Bergakademie Freiberg, Inst. f. Exp. Physik, Silbermannstr.1, 09596 Freiberg, Germany 2 Weizmann Institute of Science, Materials and Interfaces Dept., 76100 Rehovot, Israel Abstract Numerical simulations of the defect distribution of CuInSe 2 were carried out as a function of the stoichiometry. The simulations are based on a new calculation of the intrinsic defects in this ma- terial. The results of the calculations were compared with earlier electrical and positron lifetime mea- surements. This leads to the assumption, that the single defects V Se , V Cu , Cu In and the defect pair (2V Cu -In Cu ) occur in the investigated specimens in considerable concentrations. Keywords CuInSe 2 , positron lifetime, formation energy, energy level, stoichiometry, intrinsic defects Introduction The electrical and optical properties of many ternary ionic compounds such as CuInSe 2 are dominated by the presence of intrinsic point defects. These defects are related to the stoichiometry and the thermal history of the specimens. In a ternary compound at least twelve intrinsic defects (vacancies, interstitials and antisite defects) are possible, but considering that agglomerations of these defects can occur, the number may be considerably larger. In many practical applications of these compounds, the identification of the dominant defects would enhance the understanding of the properties and allows one a better control. Based on a new calculation of the formation energies of some of these defects, the defect chemistry as a function of the stoichiometry was simulated. The results of the simulations are compa- red with positron lifetime measurements in CuInSe 2 single crystals of various compositions. The po- sitron annihilation spectroscopy is a suitable method which allows one to study vacancy-like defects in solids. Positrons can be trapped in the open volume of the defects which increases their lifetime.